Amount Of Synchrony Research Articles

Altered Information Processing in the Prefrontal Cortex of Huntington's Disease Mouse Models

Understanding cortical information processing in Huntington's disease (HD), a genetic neurological disorder characterized by prominent motor and cognitive abnormalities, is key to understanding the mechanisms underlying the HD behavioral phenotype. We recorded extracellular spike activity in two symptomatic, freely behaving mouse models: R6/2 transgenics, which are based on a CBA x C57BL/6 background and show robust behavioral symptoms, and HD knock-in (KI) mice, which have a 129sv background and express relatively mild behavioral signs. We focused on prefrontal cortex and assessed firing patterns of individually recorded neurons as well as the amount of synchrony between simultaneously recorded neuronal pairs. At the single-unit level, spike trains in R6/2 transgenics were less variable and had a faster rate than their corresponding wild-type (WT) littermates but showed significantly less bursting. In contrast, KI and WT firing patterns were closely matched. An assessment of both WTs revealed that the R6/2 and KI difference could not be explained by a difference in WT electrophysiology. Thus, the altered pattern of individual spike trains in R6/2 mice appears to parallel their aggressive form of symptom expression. Both WT lines, however, showed a high proportion of synchrony between neuronal pairs (>85%) that was significantly attenuated in both corresponding HD models (decreases of approximately 20% and approximately 30% in R6/2s and knock-ins, respectively). The loss of spike synchrony, regardless of symptom severity, suggests a population-level deficit in cortical information processing that underlies HD progression.

Tremor entrainment by patterned low-frequency stimulation

High-frequency test stimulation for tremor suppression is a standard procedure for functional target localization during deep brain stimulation. This method does not work in cases where tremor vanishes intraoperatively, for example, due to general anaesthesia or due to an insertional effect. To overcome this difficulty, we developed a stimulation technique that effectively evokes tremor in a well-defined and quantifiable manner. For this, we used patterned low-frequency stimulation (PLFS), i.e. brief high-frequency pulse trains administered at pulse rates similar to neurons' preferred burst frequency. Unlike periodic single-pulse stimulation, PLFS enables one to convey effective and considerably greater integral charge densities without violation of safety requirements. In a computational investigation of an oscillatory neuronal network temporarily rendered inactive, we found that PLFS evokes synchronized activity, phase locked to the stimulus. While a stronger increase in the amount of synchrony in the neuronal population requires higher stimulus intensities, the portion of synchronously active neurons nevertheless becomes strongly phase locked to PLFS already at weak stimulus intensities. The phase entrainment effect of PLFS turned out to be robust against variations in the stimulation frequency, whereas enhancement of synchrony required precisely tuned stimulation frequencies. We applied PLFS to a patient with spinocerebellar ataxia type 2 (SCA2) with pronounced tremor that disappeared intraoperatively under general anaesthesia. In accordance with our computational results, PLFS evoked tremor, phase locked to the stimulus. In particular, weak PLFS caused low-amplitude, but strongly phase-locked tremor. PLFS test stimulations provided the only functional information about target localization. Optimal target point selection was confirmed by excellent post-operative tremor suppression.

Allelomimetic synchronization in Merino sheep

Changes between the inactive (resting/ruminating) and active (grazing, walking) states in groups of Merino sheep were studied in the field for different group sizes (two, four, six or eight) of either male or female animals over 6-h periods. The amount of synchrony within groups was high (60–80%) and is attributed to the mutual adjustment of behaviour by group members. To quantify this process, changes in the number of active individuals were fitted by a time homogeneous continuous time Markov chain model. We found that the probability of an individual becoming active increased with the number of active conspecifics in the group and decreased with the number of inactive conspecifics. The reverse effect was found for the probability of becoming inactive. A model of this individual decision-making process is fitted to the data and predictions of the model are shown to account for the synchrony observed within the group. Group synchronization is thus presented as a self-organized dynamic system, where collective oscillations between activity and inactivity arise stochastically from the coupling between individual Markov processes.

Dual task-related changes in the synchronous activity of wrist extensor type-identified motor units in humans

The coupling between the firings of 33 pairs of motor units tested in the extensor carpi radialis muscles was evaluated by cross-correlation analysis and compared during isometric wrist extension and hand clenching. A slightly greater amount of synchrony was observed during hand clenching (0.042 - 0.024 vs 0.035 - 0.017 synchronous impulses per trigger). This trend did not reach however the level of significance and the changes were actually found to be heterogeneous: in 15 out of the 33 pairs tested, synchronous activity with a narrow coupling (4.6 - 2.4 ms) consistent with short-term synchrony was greater during hand clenching whereas in nine other pairs, synchronous activity with a broader dispersion (9.0 - 4.5 ms) was reduced. These opposite changes could not be explained in terms of changes in the firing pattern of the motor units and were found instead to correlate with the motor units' biomechanical properties. Motor units with high recruitment thresholds and fast rising twitches showed predominantly an increase in synchrony; whereas the motor unit pairs with low recruitment thresholds and slow twitches showed either an increase or a decrease. The enhanced short-term synchrony suggests that common inputs distributed to motoneurones of all types were more effective during hand clenching whereas the decrease in weakly coupled synchronous activity suggests that other inputs synchronized at a pre-synaptic level and distributed more specifically to motor units recruited at low force levels were less effective. The possible origins of the inputs reflected in the dual changes are discussed in terms of the supra-spinal and peripheral pathways controlling the wrist extensor motoneurones during wrist extension and hand clenching.

Seasonal Model of the Interaction Between Rhinocyllus conicus (Coleoptera: Curculionidae) and Its Weed Host, Carduus thoermeri (Campanulatae: Asteraceae)

A computer model was developed to simulate the flowering phenology of musk thistle, Carduus thoermeri Weinmann, and the seasonal population dynamics of Rhinocyllus conicus Froelich. Time-varying distributed delays in series were used to model the populations. The model output was validated by comparison with field data. The results suggest that the population dynamics of R. conicus and musk thistle were adequately described by the model. The model could not be rejected using a nonparametric regression technique, though a low number of degrees of freedom limited the test. The amount of synchrony that the model showed between the development of plant and insect was highly sensitive to temperature. Our simulation results suggest that site specific variations in temperature can have profound effects on the temporal synchrony of parasite and host. Thus, future evaluations of parasite effectiveness should include the development of phonological models driven by data collected at or near the introduction site. Phenology models, which are quantitative, scientifically based hypotheses, should be considered as part of the evaluation of host/parasite interactions.

Bidirectional termination of chromosome replication in Escherichia coli.

Autoradiography was used to study the termination of replication of the circular chromosome of Escherichia coli. The experiments were conducted with cells in which termination occurred with a moderate amount of synchrony. Grain tracks were observed that demonstrated the approach at the replication terminus of the two replication forks involved in bidirectional replication. Other grain tracks were formed by replication forks that had met at the replication terminus. The frequency at which these patterns were observed indicates that most, if not all, terminations occur with both replication forks reaching the terminus at approximately the same time.